Means of restraint that are able to be activated irreversibly, e.g., pyrotechnically ignitable ones, such as air bags or belt pretensioners, have become standard for cars. When a situation is detected that is dangerous for a person sitting in the seat, e.g., an impact onto an obstacle, these means of restraint are triggered in order to protect the person from dangerous injury. For reasons of cost, the triggering should not occur if the seat is not occupied. Furthermore, triggering should not occur if there is not a person in the seat, but rather an object. Triggering is particularly to be avoided if the object is a baby carrier. In addition, it would be desirable to be able to have triggering procedures that are adaptable as a function of the stature of the person. Therefore, in order to avoid very unsafe, only manually operable switches, a method and a device are required which, with the greatest possible safety, are able to detect, for one, the occupancy state as such. In addition, these methods and devices, under certain circumstances also together with others, should permit distinguishing at least between objects and persons, and, if possible, also between different objects, and particularly between different persons or rather, types of persons.
For example, U.S. Pat. No. 5,570,903 describes assigning a mat to the seat surface of a seat, with the aid of which the weight of an object acting on the seat is ascertainable. By using a matrix-like system of sensors, a pressure distribution may also be ascertained, and optionally also the distance apart of the ischial tuberosities of a person. To be sure, the occupancy state is easy to ascertain, but this procedure is extraordinarily cumbersome, and also costly, since special seats are required.
U.S. Pat. No. 5,983,147 describes producing an image at least for the front passenger seat, using a stereo-video camera. The respective image may thereupon be evaluated as to whether the seat is occupied at all, and whether, if so, a person or an object is there. For the initialization of this procedure, a very cumbersome and drawn-out learning or training phase is required, since for each type of state to be detected, especially when objects and persons are to be distinguished, empirically determined training data have to be placed at disposal, and these training have first of all to be determined and entered. For the application of this, on the basis of the training data and data obtained by the image as well as appropriate algorithms, a classification is made, first according to occupancy state and then according to occupancy type. This procedure has grave disadvantages. For instance, types of occupancy that were not foreseen in the training data are not able to be recorded, which may lead under certain circumstances to serious misinterpretations, that is, erroneous classifications. Moreover, changing illumination situations, of the kind frequently appearing in daily traffic, may likewise lead to erroneous classifications. Also, in the training phase, non-trained seat parameters may lead to erroneous classifications. Finally, when a seat is exchanged, a renewed initialization has to be carried out, the corresponding training data not being available for all seats sold in the trade. Consequently, this conventional procedure based on the ascertainment of a 3D image is not only extremely costly, but is also unrelieble in the wider scope.
Accordingly, an object of the present invention is to provide an improved method and device for detecting the occupancy state and optionally also the occupancy type.